1. Field of the Invention
The present invention relates to a rechargeable battery. More particularly, it relates to a structure connecting an electrode assembly with lead elements.
2. Discussion of the Background
A rechargeable battery may be charged and discharged unlike a nonrechargeable battery that may not be recharged. A low capacity rechargeable battery that comprises a pack shaped battery cell may be used as a power source for various small portable electronic devices such as cellular phones, laptop computers, and camcorders. A high capacity rechargeable battery that has several tens of the battery cells that are connected may be used as power sources for driving motors such as hybrid automobile.
The rechargeable battery may be fabricated into various shapes including a cylindrical and a rectangular box shape and may comprise an electrode assembly comprising a positive electrode and a negative electrode and an insulating separator that is interposed in between the electrodes and is wound and inserted into a case. The case is mounted with a cap assembly that is formed with an outer terminal to provide a battery.
The positive electrode and the negative electrode are provided with a conductive lead element to collect current that is generated during a cell's operation. The lead elements transfer the current that is generated in the positive electrode and the negative electrode to a positive terminal and a negative terminal, respectively.
When the electrode assembly is integrated with the lead elements that connect the electrode assembly with the external terminals, it becomes difficult to output a voltage that is generated in each part of the electrode assembly. This causes a potential difference between the area where the electrode assembly is welded to the lead element and the area surrounding the welding area. This potential difference degrades the welding area and the degradation increases as the battery is charged repeatedly. Consequently, the output of the battery drops and the lifespan of the battery shortens. These problems are exacerbated in a battery for driving a motor which repeats charge and discharge within a short amount of time.
For this reason, multi-tabs are used as the lead elements in a high-power rechargeable battery. For example, a rechargeable battery that uses multi-tabs as lead elements is disclosed in Japanese Patent Laid-Open No. 2003-007346. Conventional rechargeable batteries that include this technology, however, weld the multi-tabs into the current collectors of the positive electrode and negative electrode or they form the multi-tabs as part of the current collectors. The use of multi-tabs decreases the manufacturing efficiency because it requires numerous workers to manufacture the secondary battery.
Also, since the multi-tab-type lead elements are partially connected to the positive electrode and negative electrode and they collect the current that is generated at the positive electrode and negative electrode, it becomes difficult to collect a sufficient amount of current, especially in a motor-driven battery that requires a high output of power. Thus, the multi-tab-type lead elements are highly likely to degrade the properties of the battery.